The present invention relates to an improved method of making a turbine engine component with slip joints which interconnect a shroud ring and a plurality of airfoils.
A known turbine engine component having slip joints which interconnect a shroud ring and a plurality of airfoils is disclosed in U.S. Pat. No. 4,728,258. This patent indicates that metallurgical bonds do no form between the ends of the airfoils and a shroud ring due to an oxide coating over the ends of the airfoils. This oxide coating over the ends of the airfoils is formed during handling of the airfoils in the atmosphere. The oxide coating is black and is believed to be a nickel, chromium, and/or aluminum oxide coating which forms as a result of exposure of the airfoil to an oxygen-containing atmosphere at relatively low temperatures. The black oxide coating has a low melting temperature relative to Cr.sub.2 O.sub.3.
When castings made by the process disclosed in U.S. Pat. No. 4,728,258 were sectioned, it was found that fusion bonds occasionally occurred at the slip joints between the end portions of the airfoils and the shroud ring. Although there were many instances when the bonding did not occur, the possibility of having a fusion bond at the slip joint reduces the degree of confidence which can be placed in the process of making the turbine engine component. Unfortunately, the presence of a bond between the end portions of the airfoils and the shroud ring cannot be easily detected without destroying the turbine engine component. Turbine engine components having slip joints between airfoils and shroud rings are also disclosed in U.S. Pat. Nos. 4,955,423 and 4,961,459.